This invention relates to traffic signal control equipment in general, and in particular to an improved traffic signal head.
Traffic signal heads are known and are used to help control the flow of vehicular traffic through a controlled intersection. A conventional signal head has three vertically disposed lamps with colored lensesxe2x80x94one red (usually positioned at an upper position of the signal head), one green (usually positioned at a lower position of the signal head) and one yellow or amber (usually positioned between the red and the green). The state of each lamp is controlled by auxiliary control circuits in accordance with a control algorithm to provide drivers with visual control directives regarding the passage of vehicles through the intersection. Illumination of the red lamp signals the driver to stop at the intersection, while illumination of the green lamp signals the driver t hat passage through the intersection is permitted. Illumination of the yellow or amber lamp signals the driver that the red lamp is about to be illuminated and cautions the driver to be prepared to stop.
Traffic signal heads of the above type have been known and used for decades and have achieved a virtually universal standard status. More recently, variations of the standard three lamp vertical configuration of signal heads have appeared. For example, signal heads have been designed with three lamps arranged in a horizontal row; and with additional lamps of each color to provide greater illumination or noticeability to the driver. All such variations use conventional incandescent lamps as the illumination source.
Even more recently, signal heads have been designed with a different light source. Due to recent improvements in the field of light emitting diode (LED) technology, LEDs have been proposed for use and have actually been implemented in signal heads as the illumination source. Compared to incandescent lamps, LEDs possess some properties which are superior to ordinary lamps. An LED is less fragile than a glass enclosed lamp, and is thus more suited to a signal head application in which the light source is exposed to potential mechanical and environmental damage. Also, an LED has a longer average life time than a conventional incandescent lamp and thus on average requires replacement less frequently. Further, an LED is more light efficient than a conventional incandescent lamp, consuming less electrical power. In addition, an LED can be manufactured to radiate light of a particular color, so that a colored or tinted lens is not required to provide the colors red, green and yellow. For these reasons, LEDs promise to become the illumination source of choice for traffic signal heads in the future.
In known traffic signal heads using LEDs as the illumination source, each single color illumination source is comprised of several monochromatic LEDs clustered together as a unit. This is necessary due to the fact that a single LED does not generate sufficient luminance to function effectively as the illumination source. All LEDs in a given monochromatic cluster are driven in parallel by the appropriate control signal in order to provide the proper visual directives to drivers. Thus, in known signal heads using LEDs, the single incandescent lamp corresponding to a given control color is replaced with a cluster of monochromatic LEDs all operated in parallel or series-parallel, and at least three clusters (one for each control color) are used to replace the at least three incandescent lamps.
U.S. Pat. No. 5,898,381, the disclosure of which is hereby incorporated by reference, discloses an improvement over the basic type of LED based signal head. In this patent, each cluster of monochromatic LEDs is arranged in the shape of a traffic symbol conventionally used with the associated color. For example, the cluster of red LEDs is arranged in an octagonal shape to simulate a conventional stop sign, the cluster of yellow LEDs is arranged in a triangular shape, and the cluster of green LEDs is arranged in a circular shape. In addition, other traffic symbols are represented by clusters of appropriately colored LEDs, such as a green or red arrow. Further, this patent discloses an additional improvement of positioning all signal head LED clusters in a single compartment, with individual LEDs of different colors being mutually interspersed throughout the compartment, so that the bulk and excessive weight of conventional signal heads is substantially reduced without sacrificing the visible functionality of such devices.
While the improvements in the art of signal head technology disclosed in the ""381 patent are significant, the need still exists for further improvements in ease of implementation, flexibility of operation, power consumption and cost.
The invention comprises a signal head which incorporates multiple LED light sources into one or more light source compartments at lowered cost and with lowered power consumption, while still providing visually distinctive multiple color driver advisory signals and symbols.
In a first apparatus aspect, the invention comprises a traffic signal head having a housing and a plurality of LED light sources mounted in the housing for providing red, yellow, and green driver advisory light signals, with each of the LED light sources comprising a first LED light element having a red light generation characteristic and a second LED light element having a green light generation characteristic. The traffic signal head includes activation circuitry for enabling individual activation of the first and second LED light elements and concurrent activation of the first and second LED light elements so that individual activation of the first LED light element produces red light, individual activation of the second LED light element produces green light, and concurrent activation of the first and second LED light elements produces yellow light.
Each of the first and second LED light elements has an anode, a cathode, an anode terminal and a cathode terminal, the cathode terminals of the first and second LED light elements being coupled together to a source of electrical power. The activation circuitry includes first and second power switching devices each having first and second power transfer terminals and a control input terminal. The first power transfer terminal of the first and second power switching devices is coupled to the source of electrical power. The second power transfer terminal of the first power switching device is coupled to the anode terminal of the first LED light element. The second power transfer terminal of the second power switching device is coupled to the anode terminal of the second LED light element. The control input terminal of the first power switching device is coupled to a source of red control signals, the control input terminal of the second power switching device is coupled to a source of green control signals, and the control input terminals of the first and second power switching devices are coupled to a source of yellow control signals. The first and second power switching devices are preferably transistors.
In an alternate embodiment of the invention, each of the LED light sources comprises an encapsulation package containing a first LED light element having a red light generation characteristic, a second LED light element having a yellow light generation characteristic, and a third LED light element having a green light generation characteristic. The traffic signal head includes activation circuitry for enabling individual activation of the first, second, and third LED light elements.
Both embodiments can serve as standard modules in a conventional three compartment signal head, or can be combined in a single compartment to provide a more compact signal head with all three color functions.
From a process standpoint, the invention comprises a method of producing driver advisory signals of different colors, the method comprising the steps of providing a traffic signal head with a plurality of LED light sources each comprising a first LED light element having a red light generation characteristic and a second LED light element having a green light generation characteristic; activating the first LED light element of the plurality of LED light sources to generate red driver advisory signals; activating the second LED light element of the plurality of LED light sources to generate green driver advisory signals; and concurrently activating the first and second LED light elements of the plurality of LED light sources to generate yellow driver advisory signals.
From an alternate process standpoint, the invention comprises a method of producing driver advisory signals of different colors, the method comprising the steps of providing a traffic signal head with a plurality of LED light sources each comprising an encapsulation package containing a first LED light element having a red light generation characteristic, a second LED light element having a yellow light generation characteristic, and a third LED light element having a green light generation characteristic; activating the first LED light element of the plurality of LED light sources to generate red driver advisory signals; activating the second LED light element of the plurality of LED light sources to generate yellow driver advisory signals; and activating the third LED light element of the plurality of LED light sources to generate green driver advisory signals.
The invention provides a traffic signal head which occupies substantially less physical volume than conventional signal heads without sacrificing any operational functionality. In addition, the embodiment of the invention employing only two-color LED light elements requires a substantially reduced number of individual LED light sources, with a commensurate reduction in cost and power consumption, while providing the same driver advisory capability as conventional signal heads. Further, both embodiments of the apparatus can serve as programmable standard modules for a traffic control system, and can be electrically configured to function as red, yellow, or green light generating devices for both the ordinary color advisory signals and special color advisory symbols, such as right or left-pointing red, yellow, or green arrows. Thus, only a single type of standard unit need be inventoried to serve the entire light source requirements of a traffic control system.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.